A plastic molded product has advantages such as light weight, impact resistance, dyability and machinability, compared with a product of glass and holds a major position in the field of lenses, particularly, lenses for eyeglasses, lenses for electronic apparatuses and the like. On the other hand, the plastic molded product has drawbacks in abrasion resistance, heat resistance and the like and, then, in order to improve these drawbacks, various types of efforts for improvements or modifications have been exerted. As a method for improving the abrasion resistance, a cured film has ordinarily been applied on a plastic substrate. The cured film ordinarily comprises a coating composition which contains a hydrolysate of an organosilane as a main component; however, when a refractive index thereof is largely different from that of the substrate, an interference fringe comes to be conspicuous to cause an inferior appearance and, for this account, the refractive index is adjusted by allowing fine particles of a metal oxide to be dispersed in the coating composition. In JP-A Nos. 2001-122621 and 2001-123115, a colloidal particle of titanium oxide as a nucleus is coated with a colloidal particle of antimony oxide to modify titanium oxide as the nucleus and, in this case, while a high refractive index which is characteristic of titanium oxide is realized, compatibility of a silane coupling with the hydrolysate and stability which are characteristic of antimony oxide are also realized.
However, even though it was tried to coat such coating composition as described above on the resin substrate and, then, to form a cured film, adhesion was insufficient, and initial adhesion and weathering resistant adhesion were by no means satisfactory for practical use. For this account, in order to impart adhesion, a two step process was necessary such that a pretreatment liquid is applied on the resin substrate and, thereafter, the coating composition was applied. Particularly, the adhesion to a polycarbonate resin substrate was poor and application of the pretreatment liquid was indispensable. Further, as to other characteristics of the polycarbonate resin, it was difficult to be dyed compared with other resins and, when it is required to dye such resins as having poor dyability, it is necessary to change the cured film to be a dyable one.
Further, in JP-A No. 06-256718, disclosed is a cured film composition which adheres to a thermoplastic sheet without being coated with the pretreatment liquid by allowing a caprolactone-based polyester polyol to be contained in the coating composition as an adhesion promoter. However, there was a problem in that this composition was insufficient in adhesion and, when an effective amount of the caprolactone-based polyester polyol for a required adhesion was contained, whitening of a resin-made composite which has been applied with the cured film was conspicuous. Such whitening phenomenon heavily deteriorates characteristics of optical products such as lenses of eyeglasses; therefore, it can not be applied to a product in which the whitening phenomenon is not desirous.
The patent documents as cited herein are as follows:
Patent Document 1: JP-A No. 2001-122621;
Patent Document 2: JP-A No. 2001-123115; and
Patent Document 3: JP-A No. 06-256718.